Since a very large load is applied in the radial direction to a rotation system in a power mechanism provided for automobiles and railroad vehicles, for example, a radial roller bearing (hereafter referred to as a roller bearing or a bearing) being superior in load capacity for the load has been used conventionally and widely as a bearing for rotatably supporting the rotation shaft thereof. Such a bearing is equipped with an outer member (for example, an outer ring or a housing being maintained in a non-rotating state at all times, or a gear, a roller, etc. being rotatable during use) having a cylindrical outer track on the inner circumferential face thereof, a plurality of rollers (for example, a plurality of needles) incorporated so as to be able to roll between the outer circumferential face (inner track) of an inner member (for example, an inner ring, a shaft, etc. being rotatable during use) disposed on the inner diameter side of the outer member and the outer track, and a cage for holding these rollers at predetermined intervals (at equal intervals as an example) in the circumferential direction and mounted on the outer member and the inner member. In addition, the cage is configured so as to be equipped with a pair of circular ring sections opposed to each other coaxially with a predetermined clearance provided therebetween and a plurality of pillar sections for connecting these, for separating the area between the circular ring sections in the circumferential direction of the circular ring sections and for forming pockets in which the rollers are inserted and held rotatably.
Conventionally, for example, a needle roller bearing (needle bearing) is known as a bearing capable of being improved in load capacity by virtue of numerous rolling elements (rollers) incorporated while being made compact. Furthermore, a measure for preventing fretting during bearing rotation is taken for the needle roller bearing, and a single-split cage is applied as an example of the preventive measure in some cases (for example, refer to Patent documents 1 and 2).
For example, the single-split cage 2 shown in FIG. 25 is equipped with a pair of circular ring sections 4 and 6 having a circular ring shape and being disposed so as to be opposed to each other and a plurality of pillar sections 8 continuously extending between the circular ring sections 4 and 6 and arranged at predetermined intervals (for example, at equal intervals) in the circumferential direction. In this case, a plurality of space regions are formed at predetermined intervals (for example, at equal intervals) in the circumferential direction in the portions enclosed by the pillar sections 8 being adjacent in the circumferential direction and the pair of circular ring sections 4 and 6, and the plurality of space regions are formed as a plurality of pockets 2p for rotatably holding rolling elements (rollers), one by one. As a result, in the single-split cage 2, the plurality of rolling elements (rollers) are held at predetermined intervals (for example, at equal intervals) in the circumferential direction.
In the single-split cage 2, the rolling elements (rollers) being held in the respective pockets 2p are herein configured as slender rollers having a small diameter and a length 3 to 10 times the diameter. Furthermore, the single-split cage 2 is, for example, incorporated between inner and outer rings while rotatably holding the rolling elements (rollers) in the respective pockets 2p, one by one, and, in this state, revolves along the tracks between the inner and outer rings together with the rolling elements (rollers) during bearing rotation. The single-split cage 2 is entirely molded (for example, injection molded) with a resin (for example, thermoplastic resin).
Moreover, in the single-split cage 2, a split section for dividing the cage at one portion located in the circumferential direction in a direction being crosswise to (perpendicular to) the circumferential direction is provided. The split section 10 is formed in regions (hereafter referred to as split regions 10a and 10b) extending between the pockets 2p being adjacent to each other in the circumferential direction, and one-side split face Sa and the other-side split face Sb configured by the splitting of the two regions, the split regions 10a and 10b, are disposed so as to be opposed to each other in the circumferential direction. In this case, the pair of circular ring sections 4 and 6 extends, while having a circular ring shape, from the one-side split region 10a on which the one-side split face Sa is formed to the other-side split region 10b on which the other-side split face Sb is formed.
Besides, on the one-side split face Sa, a rectangular convex section 12 protruding (extending) toward the other-side split face Sb from a part of the central portion thereof is provided; on the other hand, on the other-side split face Sb, a concave section 14 formed by denting a part thereof into a rectangular shape so that the convex section 12 can be inserted therein and engaged therewith is provided. This prevents, for example, dislocation between the split faces Sa and Sb when the single-split cage 2 is incorporated between the inner and outer rings (more specifically, dislocation of the single-split cage 2 revolving along the tracks between the inner and outer rings during bearing rotation in the direction of the rotation axis Z of the single-split cage 2).
Furthermore, Patent document 2 discloses a single-split cage in which a convex section is provided on one-side split face of the split faces of the cage and a concave section is provided on the other-side split face and the respective end faces thereof are formed into a tapered shape so that the convex and concave sections having been engaged once are not disengaged in the circumferential direction.
A case is herein assumed as an example in which a cage for use in a bearing having an outer ring as an outer member and a rotation shaft as an inner member is mounted in the inner track portion of the rotation shaft. In this case, the cage is inserted from the end section of the rotation shaft and moved to the inner track portion of the shaft in the axial direction. At the time, in the case that step sections and flange sections having outer diameters larger than the inner diameter of the cage are provided so as to protrude in the outer circumferential range of the shaft from the end section of the shaft to the inner track, the inner circumferential section of the cage interferes with these step sections and flange sections, and the cage cannot be moved to the inner track portion in the axial direction.
Hence, for the purpose of solving this problem, a configuration of a cage in which a part of the cage made of a resin is equipped with a split section, in other words, a configuration of a cage in which each of a pair of circular ring sections (rim sections) is formed into a discontinuous nearly circular ring shape (deficit circular ring shape) having a slit (deficit section) at a part thereof (one position, as an example) is known conventionally (refer to Patent document 3 and Patent document 4). With this kind of configuration, the split section can be expanded and the cage can be increased in diameter by exerting a force to the cage in the circumferential direction so that both circumferential end faces (the faces opposed to each other at the deficit section) of the circular ring sections (rim sections) are separated.
As a result, for example, even in the above-mentioned case that the step sections and flange sections having outer diameters larger than the inner diameter of the cage are provided so as to protrude in the outer circumferential range of the shaft, when the split section of the cage is expanded (the cage is increased in diameter), the cage can be moved smoothly to the inner track portion of the rotation shaft in the axial direction without interfering with the step sections and the flange sections.
Furthermore, after the cage is moved to the inner track portion of the rotation shaft, when a force is exerted to the cage so that both end faces (the opposed faces at the deficit section) of the respective circular ring sections (rim sections) in the circumferential direction are brought close to each other in the circumferential direction, whereby the split section is shrunk (returned to its original state before expansion) and the diameter of the cage is returned to the original state. Hence, the cage is mounted on the inner track portion of the rotation shaft. At the time, a predetermined engagement mechanism is provided on the opposed faces of the pillar sections adjacent to each other in the circumferential direction with the split section provided therebetween so that the split section of the cage is not expanded again. For example, as such an engagement mechanism, a convex section is provided on one opposed face so as to protrude toward the other opposed face; furthermore, a concave section is provided on the other opposed face so that the convex section can be fitted therein; when the convex section and the concave section are fitted to each other and positioned, both the opposed faces are engaged with each other and the split section is prevented from being expanded again.
In the cage disclosed in Patent document 3, for the pair of the circular ring sections (rim sections), on the opposite side of the deficit section with respect to the center of the circular ring sections, that is, at the outer circumferential portions dislocated by 180° in phase with respect to the deficit section in the circumferential direction, a single groove (slit) is provided so as to be concave in a nearly V-shape in a cross-sectional view in the axial direction, and on the outer circumferential face of the pillar section for connecting the portions, a single groove (slit) communicating with the groove in the circular ring sections (rim sections) is also provided so as to be concave in a nearly V-shape in a cross-sectional view in the axial direction.
Since the grooves are provided in the circular ring sections (rim sections) and the pillar section, in the case that a force is exerted in the circumferential direction to the cage so that both end faces (the opposed faces in the deficit section) of the circular ring sections (rim sections) are separated from each other, while the grooves in the circular ring sections (rim sections) and the pillar section are used as fulcrums, the cage is elastically deformed so that the grooves are collapsed. Hence, the split section can be expanded easily, that is, the cage can be increased in diameter easily. Furthermore, in the cage disclosed in Patent document 4, the inner circumferential sections of a pair of circular ring sections (rim sections) are made larger in diameter than the inner circumferential sections of pillar sections along the entire circumference and made thinner than the pillar sections in the radial direction, whereby the split section thereof can be expanded easily, that is, the cage can be increased in diameter easily.